Recently, electronic apparatuses which can be powered by battery and carried easily, such as tablet computers and smartphones, have become widespread. At the same time, electronic apparatuses of the type which are worn on a human body in the form of, for example, wristwatch and glasses, which are referred to as wearable devices, etc., have been developed. Some of these wearable devices can obtain physiological information on a user wearing the wearable device, such as a pulse and percutaneous arterial blood oxygen saturation (SpO2).
As a method of acquiring the physiological information such as the pulse and SpO2, a method of irradiating light onto the human body and analyzing the light which has been reflected from or has passed through the body is known. This method uses a difference in absorptivity of the light beams of specific wavelengths (typically, red light and infrared light) between oxyhemoglobin and deoxyhemoglobin in the blood.
A device which acquires the physiological information by this method is easily affected by movement of the human body (which may be hereinafter referred to as body motion), and accuracy of the physiological information which is acquired in a state where the body motion is large is decreased. As countermeasures against body motion, one idea is to irradiate light beams of many more different wavelengths onto the human body in order to acquire the physiological information accurately even in a situation where the body motion is large.
Meanwhile, the wearable device is required to be small and light in terms of the feature that it is worn on the human body, and the battery capacity for supplying operating power is also limited. Accordingly, achieving low power consumption in the wearable device is strongly required.